EP0096824B1 - Fine focus x-ray tube and method for the production of a finely focused electron emission from an x-ray filament cathode - Google Patents

Fine focus x-ray tube and method for the production of a finely focused electron emission from an x-ray filament cathode Download PDF

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Publication number
EP0096824B1
EP0096824B1 EP83105571A EP83105571A EP0096824B1 EP 0096824 B1 EP0096824 B1 EP 0096824B1 EP 83105571 A EP83105571 A EP 83105571A EP 83105571 A EP83105571 A EP 83105571A EP 0096824 B1 EP0096824 B1 EP 0096824B1
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Prior art keywords
cathode
ray tube
wire
electron
focus
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EP83105571A
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German (de)
French (fr)
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EP0096824A1 (en
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Alfred Dipl.-Ing. Reinhold
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Feinfocus Verwaltungs & Co KG GmbH
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Feinfocus Verwaltungs & Co KG GmbH
Feinfocus Verwaltungs & Co KG GmbH
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J35/00—X-ray tubes
    • H01J35/02—Details
    • H01J35/14—Arrangements for concentrating, focusing, or directing the cathode ray
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J35/00—X-ray tubes
    • H01J35/02—Details
    • H01J35/04—Electrodes ; Mutual position thereof; Constructional adaptations therefor
    • H01J35/06—Cathodes
    • H01J35/064—Details of the emitter, e.g. material or structure
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J35/00—X-ray tubes
    • H01J35/02—Details
    • H01J35/04—Electrodes ; Mutual position thereof; Constructional adaptations therefor
    • H01J35/06—Cathodes
    • H01J35/066—Details of electron optical components, e.g. cathode cups

Definitions

  • the invention relates to a fine focus X-ray tube, in the evacuated piston of which is housed a hot cathode partially surrounded by a rotationally symmetrical control electrode, formed by a heating wire, and an anode equipped with a target, electromagnetic electron beam focusing and deflection devices and an inlet aperture, and a method for forming a microfocus Electron emission.
  • the X-ray tube mentioned in the introduction has become known from US-A-41 59 436.
  • a hot cathode formed from a V-shaped wire is provided here, which is surrounded by a hollow cylinder with a front internal protrusion as a control electrode, special means for forming a microfocus are not provided here, however, because problems of improving the insulation and problems are involved electrostatic or electromagnetic focusing.
  • the greatly shortened service life of the hot cathode means that it must be replaced frequently, a process in which the X-ray blush has to be evacuated again before it is ready for use again. This is a time-consuming process that affects the ratio of usage time to downtime very unfavorably.
  • the invention is based on the finding that the longer the cross-section of the filament and the lower its temperature, at least at the surface, the longer the service life of a hot cathode, and that a microfocus can be formed on this surface of a relatively thick wire if it is only possible to expose a location of the surface to special physical conditions that do not exist on other parts of the surface and that are preferably suitable for electron emission.
  • the invention consists in that the cross-sectional dimensions of the wire of the hot cathode are large compared to the dimensions of the electron exit surface and that a device for achieving an increased surface temperature is provided at the point at which the electric field between the anode and cathode reaches its highest value.
  • control electrode offers itself as a simple component that is present anyway if it is only dimensioned in a suitable manner.
  • the glow wire is cooled (to different extents) in such a way that the highest temperature prevails on the surface of the glow wire at the location of the electron exit surface.
  • the device for achieving an elevated temperature is a device which strongly absorbs heat radiation and which partially surrounds the hot cathode. Because with this device, an enormous increase in the intensity of the electron emission can be achieved with the least effort.
  • This device can be the control electrode present in the X-ray tube anyway, if it is only adapted in a special way to this purpose of heat absorption.
  • a fine focus X-ray tube is characterized in that the control electrode is designed as a thick-walled body which has the shape of a hollow cylinder with an inward projection on the end face, the outside of which widens in a funnel shape, this funnel having an angle of 100 ° to Includes 140 °, and that the hot cathode with its most emerging from the inside of the control electrode in the axis of the control electrode is arranged in a plane which is in the region of the lower edge of the funnel-shaped part of the end face.
  • the hot cathode can be designed such that the hot cathode consists of a U-shaped or V-shaped wire.
  • the control electrode which acts as a cooling device, a tiny spot is then formed in the tip of the bend in the filament, which is least affected by the cooling effect and which, because it is also located at the location of the highest field strength, is a location of particularly intense electron emission .
  • a microfocus is achieved on a by no means pointed electrode of previously unsuitable shape and size, the efficiency of the emission of which significantly exceeds the pointed shaped known electrodes.
  • the cooling effect of the surface parts of the hot cathode is the cause of the significant increase in the life of the hot cathode.
  • a further increase in the intensity of the X-rays, which goes far beyond what is to be expected after the increase in electron emission, can be achieved in that the target has a spherically curved surface and the target angle has a value between 0 ° and 10 °.
  • the interaction of the measures according to the invention on the cathode with the measures according to the invention on the anode shows an increase in intensity by more than an order of magnitude, without any particular effort being made and without a loss in service life.
  • the piston of the X-ray tube consists of two parts 1, 2.
  • Part 1 takes the cathode, consisting of the filament 3, which serves as an emitter for the electron current 11, the contacts 12, 13 for the filament 3 and the base 14 and the control electrode 4, which is also carried by the base 14 and which is connected via the connection contact 15 to a voltage source, not shown.
  • the part 2 serving as the anode accommodates in its interior focusing coils 5, deflection coils 6 provided with an air gap 26 and is provided with the target head 7, which receives the target 8 (the anti-cathode) and a shield 16 in its interior, which provides an opening for has the exit of the X-rays 10 generated at the target 8, which exit through the exit window 9.
  • the target head is cooled by a cooling liquid which enters or exits a cooling chamber through the tubes 17.
  • the piston of the x-ray tube has a vacuum connection 18.
  • the electrical connections for the focusing coil 5 and the deflection coils 6 are designated 19 to 22.
  • FIG. 2 is an enlarged view of the Structure of cathode and control electrode shown.
  • the filament 3 Via the connection contacts 12, 13, which end in clamping devices 27, 28 for the U-shaped filament (emitter) 3, the filament 3 is supplied with voltage, which makes this filament glow.
  • the two clamping devices 27, 28 are accommodated in a holder 29 which also supports the grating 4 by means of the insulating ring 30.
  • This control electrode 4 is designed as a thick-walled hollow cylinder which has on its one end, surrounding the filament 3, an inward projection 34, which is formed on the outside in the form of a funnel 31, which has an opening angle ⁇ of 100 ° to 140 ° , preferably 120 °.
  • This funnel 31 merges on its inside into a cylindrical surface 32, the rounded edge 33.
  • the control electrode 4 ensures that more radiation is emitted from all surface parts of the filament 3 to the control electrode than from that location of the filament at which the geometric axis breaks through the surface of the heating wire 3 facing the target. As a result, the surface of the heating wire is cooled everywhere, but the cooling is lowest at the location at which the geometric axis 36 breaks through the surface of the heating wire facing the target 8.
  • the diameter D of the heating wire is chosen to be more than 0.17 mm, the inner radius Ri of the curvature is selected to be greater than 0.1 D. These dimensions are significantly larger than the dimensions previously used for fine focus X-ray tubes.
  • the inner radius Ri and the outer radius Ra can also have significantly larger values.
  • This apron 37 is expediently produced in one piece with the control electrode 4 and essentially represents a solid hollow cylinder.
  • FIG. 3 shows the detail 1 from FIG. 1, namely a part of the target head 7 and the target 8 in cross section.
  • the target 8 is designed as a solid block, which has a cylindrical or spherical surface on the side facing the electron stream 11.
  • the inside of the target head 7 is provided with a lining 16 made of lead.
  • the target head 7 has a lateral opening which is closed by the radiation exit window 9 for the emerging X-rays 10.
  • the values set on the target 8 are explained in more detail with reference to FIG. 4:
  • the electron beam axis E of the electron beam with the electron beam diameter De runs parallel to the tube axis 36.
  • the point of impact of the electron beam axis E and the target radius of curvature R is chosen so that a target angle a of 10 ° results. Since, with the measures according to the invention, a very thinly focused electron beam already hits the target 8, the optical focal spot width BFo is very small.
  • the hot cathode need not necessarily consist of a current-carrying wire, it can also be heated indirectly, e.g. B. are heated inductively. In this case, too, it is important that the cross-sectional dimensions of the hot cathode, which may well have the shape of a needle, are large compared to the dimensions of the electron exit area and that a point with a higher surface temperature than the other surface parts is present on the hot cathode at which the electric field between anode and cathode reaches its highest value. However, there are also ways of heating the cathode both directly through a current flowing through it and additionally indirectly.

Abstract

In an X-ray tube having a glow cathode for emitting an electron beam, an anode, focusing and deflecting coils and a target in an evacuated envelope, the cathode is a U-bent filament the dimensions of which are large in relation to the electron emitting area. The cathode is heated by passing electric current through it and is differentially cooled so that a small surface area at the site of electron emission is at a substantially higher temperature than remaining surface areas of the cathode. Cooling is effected by a thick-walled cylindrical grid which surrounds the cathode and has at its outer end an annular inward projection which absorbs heat rays from the cathode. The grid has a funnel-shaped outer end surface having an included angle of about 100 DEG to 140 DEG . The electron emitting surface of the cathode lies approximately in a plane defined by the inner peripheral edge of the funnel-shaped end surface of the grid. The electric field applied to the cathode has its highest value at the small electron emitting surface of the cathode.

Description

Die Erfindung betrifft eine Feinfocus-Röntgenröhre, in deren evakuiertem Kolben eine von einer rotationssymmetrischen Steuerelektrode teilweise umgebene, durch einen Heizdraht gebildete Glühkathode und eine mit Target, elektromagnetischen Elektronenstrahlbündelungs- und ablenkungsvorrichtungen und einer Eintrittsblende ausgestattete Anode untergebracht sind sowie ein Verfahren zur Bildung eines Mikrofocus der Elektronenemission.The invention relates to a fine focus X-ray tube, in the evacuated piston of which is housed a hot cathode partially surrounded by a rotationally symmetrical control electrode, formed by a heating wire, and an anode equipped with a target, electromagnetic electron beam focusing and deflection devices and an inlet aperture, and a method for forming a microfocus Electron emission.

Die eingangs genannte Röntgenröhre ist aus der US-A-41 59 436 bekannt geworden. Hier ist zwar eine aus einem V-förmig gebogenen Draht gebildete Glühkathode vorgesehen, die von einem Hohlzylinder mit stirnseitigem Innenvorsprung als Steuerelektrode umgeben ist, besondere Mittel zur Bildung eines Mikrofocus sind hier jedoch nicht vorgesehen, weil es hier um Probleme der Verbesserung der Isolation und Probleme der elektrostatischen oder elektromagnetischen Fokussierung geht.The X-ray tube mentioned in the introduction has become known from US-A-41 59 436. Although a hot cathode formed from a V-shaped wire is provided here, which is surrounded by a hollow cylinder with a front internal protrusion as a control electrode, special means for forming a microfocus are not provided here, however, because problems of improving the insulation and problems are involved electrostatic or electromagnetic focusing.

Aus der US-A-35 64 317, Fig. 3, ist es bekannt geworden, eine wendelförmige Glühkathode von einem ringförmigen Metallklotz als Kathodenkappe zu umgeben. Die durch die Glühkathode erzeugte Hitze kann über diesen ringförmigen Metallklotz abgeführt werden. Mittel zur Bildung eines Mikrofocus sind hier aber nicht vorgesehen, vielmehr sind durch die senkrechte Lage der Wendel zur Elektronenstromrichtung eine Reihe von Emissionsstellen nebeneinander angeordnet. Zu einer Erhöhung des Auflösungsvermögens ist es aber notwendig, eine einzige Emissionsstelle zu haben und diese nach Möglichkeit in ihren Flächenausdehnungen so klein zu machen, wie es nur irgend möglich ist.From US-A-35 64 317, Fig. 3, it has become known to surround a helical hot cathode by an annular metal block as a cathode cap. The heat generated by the hot cathode can be dissipated via this ring-shaped metal block. Means for forming a microfocus are not provided here, however, rather a number of emission points are arranged next to one another due to the vertical position of the filament in relation to the electron current direction. To increase the resolving power, however, it is necessary to have a single emission point and, if possible, to make it as small as possible in terms of its surface area.

In dem Bestreben, das Auflösungsvermögen bei Röntgengeräten zu steigern, um immer kleinere Details in Röntgenaufnahmen zu erkennen, z. B. feinste Haarrisse in Turbinenschaufeln, wurden Röntgenröhren entwickelt, deren Glühkathoden aus immer feineren Drähten hergestellt wurden und die wie spitze Nadeln geformt wurden, um die Elektronenaustrittsfläche - an der Nadelspitze - möglichst klein zu gestalten. Nur so glaubte man bisher der Regel aus der Optik, - je kleiner und punktförmiger die Lichtquelle, umso höher das Auflösungsvermögen -, entsprechen zu können und scharfe Röntgenbildaufnahmen erzielen zu können.In an effort to increase the resolving power of X-ray machines in order to recognize ever smaller details in X-rays, e.g. For example, the finest hairline cracks in turbine blades, X-ray tubes were developed, the hot cathodes of which were made from ever finer wires and which were shaped like pointed needles in order to make the electron exit area - at the tip of the needle - as small as possible. This is the only way to believe that the rule from optics - the smaller and more punctiform the light source, the higher the resolving power - was able to correspond and to be able to obtain sharp X-ray images.

Es gelingt auch, auf diesem Wege das Auflösungsvermögen eines Röntgengerätes erheblich zu steigern, doch nur um den Preis einer geringeren Elektronenemission und um den Preis einer stark verkürzten Lebensdauer der Glühkathode. Die geringere Elektronenemission führt dazu, daß man in der medizinischen Anwendung von Röntgengeräten längere Expositionszeiten benötigt und dadurch den Patienten stärker belastet, während in der Anwendung von Röntgengeräten zur Materialprüfung dem Durchdringungsvermögen Grenzen gesetzt sind, die Untersuchungen erheblich längere Zeit in Anspruch nehmen und die Einsatzmöglichkeiten am bewegten Untersuchungsobjekt erheblich eingeschränkt werden. Die stark verkürzte Lebensdauer der Glühkathode macht deren häufiges Auswechseln erforderlich, ein Vorgang, bei dem nach dem Auswechseln die Röntgenröte erst wieder evakuiert werden muß, ehe sie erneut einsatzbereit ist. Das ist ein zeitaufwendiger Vorgang, der das Verhältnis von Benutzungszeit zu Stillstandszeit sehr ungünstig beeinflußt.It is also possible to significantly increase the resolving power of an X-ray device in this way, but only at the price of a lower electron emission and at the price of a greatly shortened life of the hot cathode. The lower electron emission means that longer exposure times are required in the medical application of X-ray devices and thus put more strain on the patient, while in the use of X-ray devices for material testing the penetration capacity is limited, the examinations take considerably longer time and the possible uses moving examination object can be significantly restricted. The greatly shortened service life of the hot cathode means that it must be replaced frequently, a process in which the X-ray blush has to be evacuated again before it is ready for use again. This is a time-consuming process that affects the ratio of usage time to downtime very unfavorably.

Maßnahme am Target der Röntgenröhre zur Verbesserung der Auflösung führten weder zur Vermeidung der aufgezeigten Nachteile an der Kathode noch zu einer wesentlichen Verbesserung der Intensität der emittierten Röntgenstrahlen, wohl aber zu einem vorzeitigen Verschleiß der Targetoberfläche. Hier am Target hielt die Fachwelt bisher strikt die von Heel aufgestellte Regel ein, daß der Targetwinkel (Winkel zwischen der Senkrechten zur Elektroneneinfallsrichtung und der Targetoberfläche) zwischen 10° und 40° liegen solle, weil bei 30° bis 33° Targetwinkel ein Maximum der Intensität der Röntgenstrahlungsabstrahlung liegt. Da hier am Target keine Verbesserungen möglich erschienen, richteten sich die Versuche zur Verbesserung der Intensität auf die Kathode der Röntgenröhren und endeten an den aufgezeigten Grenzen.Measures on the target of the X-ray tube to improve the resolution did not lead to avoiding the disadvantages shown on the cathode or to a substantial improvement in the intensity of the emitted X-rays, but did lead to premature wear of the target surface. Here at the target, the experts strictly adhered to the rule established by Heel that the target angle (angle between the perpendicular to the electron incidence direction and the target surface) should be between 10 ° and 40 °, because at 30 ° to 33 ° target angle there is a maximum of intensity the X-ray radiation. Since no improvements seemed possible at the target, the attempts to improve the intensity were directed towards the cathode of the X-ray tubes and ended at the limits shown.

Es ist die Aufgabe der Erfindung, die Intensität der Elektronenemission aus einem Mikrofocus einer Glühkathode bei gleichzeitiger Steigerung deren Lebensdauer erheblich zu erhöhen und die Intensität der Röntgenstrahlenemission zu steigern.It is the object of the invention to considerably increase the intensity of the electron emission from a microfocus of a hot cathode while increasing its service life and to increase the intensity of the X-ray emission.

Der Erfindung liegt die Erkenntnis zugrunde, daß die Lebensdauer eine Glühkathode umso höher ist, je stärker der Querschnitt des Glühdrahtes ist und umso niedriger dessen Temperatur zumindest an der Oberfläche ist, und daß auf dieser Oberfläche eines relativ dicken Drahtes sich ein Mikrofocus ausbilden läßt, wenn es nur gelingt, einen Ort der Oberfläche besonderen physikalischen Bedingungen auszusetzen, die an anderen Teilen der Oberfläche nicht herrschen und die zur Elektronenemission bevorzugt geeignet sind.The invention is based on the finding that the longer the cross-section of the filament and the lower its temperature, at least at the surface, the longer the service life of a hot cathode, and that a microfocus can be formed on this surface of a relatively thick wire if it is only possible to expose a location of the surface to special physical conditions that do not exist on other parts of the surface and that are preferably suitable for electron emission.

Die Erfindung besteht darin, daß die Querschnittsdimensionen des Drahtes der Glühkathode groß gegenüber den Dimensionen der Elektronenaustrittsfläche sind und daß eine Vorrichtung zur Erzielung einer erhöhten Oberflächentemperatur an derjenigen Stelle vorgesehen ist, an der das elektrische Feld zwischen Anode und Kathode seinen höchsten Wert erreicht.The invention consists in that the cross-sectional dimensions of the wire of the hot cathode are large compared to the dimensions of the electron exit surface and that a device for achieving an increased surface temperature is provided at the point at which the electric field between the anode and cathode reaches its highest value.

Auf diese Weise erreicht man, daß trotz der Verwendung eines sehr stabilen Glühdrahtes, der infolge seiner Querschnittsgröße und seiner Oberflächentemperatur eine lange Lebensdauer aufweist, ein Mikrofokus geschaffen ist, der sich durch eine besonders hohe Intensität der Elektronenemission auszeichnet. Durch die Anordnung der Elektronenemissionsstelle in zwei Feldern, einem elektrischen Feld und einem Temperaturfeld an der Oberfläche des Glühdrahtes, deren Spitzenwerte an ein und denselben Ort fallen, läßt sich auf dem Glühdraht ein Fokus intensiver Elektronenemission von sehr kleinen Abmessungen schaffen, obwohl der Durchmesser des Glühdrahtes viel größer ist.In this way it is achieved that, despite the use of a very stable filament, which has a long life due to its cross-sectional size and its surface temperature, a microfocus is created which is characterized by a particularly high intensity of the electron emission. By the arrangement the electron emission point in two fields, an electric field and a temperature field on the surface of the filament, the peak values of which fall in one and the same place, a focus of intense electron emission of very small dimensions can be created on the filament, although the diameter of the filament is much larger .

Dabei braucht man den winzigen Fleck erhöhter Temperatur nicht einmal durch äußere Strahlungseinwirkung, z. B. durch Lichteinstrahlung, Infraroteinstrahlung oder mittels eines Lasers, zu schaffen, dieser Ort erhöhter Temperatur läßt sich viel einfacher, aber ebenso wirkungsvoll dadurch schaffen, daß man die Glühkathode mit einem Wärmestrahlung absorbierenden Körper so (teilweise) umgibt, daß von allen Orten der Oberfläche des Glühdrahtes mehr Strahlung absorbiert wird als von dem Ort der Elektronenaustrittsfläche. Hierzu bietet sich die Steuerelektrode (Gitter) als einfaches, sowieso vorhandenes Bauelement an, wenn man es nur in geeigneter Weise dimensioniert.You don't even need the tiny spot of elevated temperature due to external radiation, e.g. B. by exposure to light, infrared radiation or by means of a laser, this place of elevated temperature can be created much easier, but just as effectively, by surrounding the hot cathode with a heat-absorbing body in such a way that from all places on the surface the filament absorbs more radiation than the location of the electron exit surface. For this purpose, the control electrode (grid) offers itself as a simple component that is present anyway if it is only dimensioned in a suitable manner.

Durch diese Strahlungsabsorption, aber auch mit anderen Maßnahmen der Kühlung läßt sich erreichen, daß man den Glühdraht so (unterschiedlich stark) kühlt, daß am Ort der Elektronenaustrittsfläche die höchste Temperatur an der Oberfläche des Glühdrahtes herrscht.Through this radiation absorption, but also with other measures of cooling, it can be achieved that the glow wire is cooled (to different extents) in such a way that the highest temperature prevails on the surface of the glow wire at the location of the electron exit surface.

Dabei ist es,zweckmäßig, wenn die Vorrichtung zur Erzielung einer erhöhten Temperatur eine Wärmestrahlung stark absorbierende Vorrichtung ist, welche die Glühkathode teilweise umgibt. Denn mit dieser Vorrichtung läßt sich bei geringstem Aufwand eine enorme Steigerung der Intensität der Elektronenemission erzielen.It is expedient if the device for achieving an elevated temperature is a device which strongly absorbs heat radiation and which partially surrounds the hot cathode. Because with this device, an enormous increase in the intensity of the electron emission can be achieved with the least effort.

Diese Vorrichtung kann die sowieso in der Röntgenröhre vorhandene Steuerelektrode sein, wenn sie nur in besonderer Weise diesem Zweck der Wärmeabsorption angepaßt ist. Eine solche Feinfokus-Röntgenröhre zeichnet sich dadurch aus, daß die Steuerelektrode als ein starkwandiger Körper ausgebildet ist, der die Form eines Hohlzylinders mit an der Stirnseite nach innen gerichteten Vorsprung aufweist, dessen Außenseite sich trichterförmig erweitert, wobei dieser Trichter einem Winkel von 100° bis 140° einschließt, und daß die Glühkathode mit ihrer am weitesten aus dem Inneren der Steuerelektrode austretenden Stelle in der Achse der Steuerelektrode in einer Ebene angeordnet ist, die im Bereich der Unterkante des trichterförmigen Teiles der Stirnseitenfläche liegt.This device can be the control electrode present in the X-ray tube anyway, if it is only adapted in a special way to this purpose of heat absorption. Such a fine focus X-ray tube is characterized in that the control electrode is designed as a thick-walled body which has the shape of a hollow cylinder with an inward projection on the end face, the outside of which widens in a funnel shape, this funnel having an angle of 100 ° to Includes 140 °, and that the hot cathode with its most emerging from the inside of the control electrode in the axis of the control electrode is arranged in a plane which is in the region of the lower edge of the funnel-shaped part of the end face.

In dieser Röntgenröhre kann die Glühkathode so ausgeführt sein, daß die Glühkathode aus einem U- oder V-förmig gebogenen Draht besteht. In Zusammenwirken mit der als Kühlvorrichtung wirkenden Steuerelektrode bildet sich dann in der Spitze der Biegung des Glühdrahtes ein winziger Fleck aus, der von der Kühlwirkung am wenigsten erfaßt wird und der, da er gleichzeitig am Ort der höchsten Feldstärke liegt, ein Ort besonders intensiver Elektronenemission ist. So wird hier an einer keineswegs spitzen Elektrode von bisher ungeeignet erscheinender Form und Größe ein Mikrofokus erzielt, dessen Wirkungsgrad der Emission die spitzgeformten bekannten Elektroden wesentlich übertrifft. Die Kühlwirkung gerade der Oberflächenteile der Glühkathode ist die Ursache für die bedeutende Erhöhung der Lebensdauer der Glühkathode.In this x-ray tube, the hot cathode can be designed such that the hot cathode consists of a U-shaped or V-shaped wire. In cooperation with the control electrode, which acts as a cooling device, a tiny spot is then formed in the tip of the bend in the filament, which is least affected by the cooling effect and which, because it is also located at the location of the highest field strength, is a location of particularly intense electron emission . In this way, a microfocus is achieved on a by no means pointed electrode of previously unsuitable shape and size, the efficiency of the emission of which significantly exceeds the pointed shaped known electrodes. The cooling effect of the surface parts of the hot cathode is the cause of the significant increase in the life of the hot cathode.

Eine weitere Steigerung der Intensität der Röntgenstrahlung, die weit über das hinausgeht, was nach der Steigerung der Elektronenemission zu erwarten ist, ist dadurch erreichbar, daß das Target eine sphärisch gekrümmte Oberfläche aufweist und der Targetwinkel einen Wert zwischen 0° und 10° hat. Hier zeigt das Zusammenwirken der erfindungsgemäßen Maßnahmen an der Kathode mit den erfindungsgemäßen Maßnahmen an der Anode eine Steigerung der Intensität um mehr als eine Größenordnung, ohne daß ein besonderer Aufwand getrieben wurde und ohne daß eine Einbuße an Lebensdauer entsteht.A further increase in the intensity of the X-rays, which goes far beyond what is to be expected after the increase in electron emission, can be achieved in that the target has a spherically curved surface and the target angle has a value between 0 ° and 10 °. Here, the interaction of the measures according to the invention on the cathode with the measures according to the invention on the anode shows an increase in intensity by more than an order of magnitude, without any particular effort being made and without a loss in service life.

Das erfindungsgemäße Verfahren ist durch die Ansprüche 6 bis 8 gekennzeichnet.The method according to the invention is characterized by claims 6 to 8.

Das Wesen der Erfindung ist nachstehend anhand eines in der Zeichnung schematisch dargestellten Ausführungsbeispieles näher erläutert.The essence of the invention is explained below with reference to an embodiment shown schematically in the drawing.

Es zeigen :

  • Figur 1 einen Querschnitt durch die Feinfokus-Röntgenröhre,
  • Figur 2 einen Querschnitt durch die Kathode und die Anordnung der Steuerelektrode (Gitters),
  • Figur 3 einen Querschnitt durch einen Teil der Röntgenröhre im Bereich des Targets,
  • Figur 4 einen Teil des Targets,
  • Figur 5 eine andere Ausbildung des Glühdrahtes,
  • Figur 6 eine weitere Ausbildung des Glühdrahtes.
Show it :
  • FIG. 1 shows a cross section through the fine focus X-ray tube,
  • FIG. 2 shows a cross section through the cathode and the arrangement of the control electrode (grid),
  • FIG. 3 shows a cross section through part of the X-ray tube in the region of the target,
  • FIG. 4 shows part of the target,
  • FIG. 5 shows another design of the filament,
  • Figure 6 shows a further embodiment of the filament.

Der Kolben der Rontgenröhre besteht aus zwei Teilen 1, 2. Das Teil 1 nimmt die Kathode, bestehend aus dem Heizfaden 3, der als Emitter für den Elektronenstrom 11 dient, den Anschlußkontakten 12, 13 für den Heizfaden 3 und dem Sockel 14 und die Steuerelektrode 4 auf, welches ebenfalls vom Sockel 14 getragen wird und welches über den Anschlußkontakt 15 mit einer nicht dargestellten Spannungsquelle verbunden ist. Das als Anode dienende Teil 2 nimmt in seinem Inneren mit einem Luftspalt 26 versehene Fokussierspulen 5, Ablenkspulen 6 auf und ist mit dem Targetkopf 7 versehen, der in seinem Inneren das Target 8 (die Antikathode) und eine Abschirmung 16 aufnimmt, die eine Durchbrechung für den Austritt der am Target 8 erzeugten Röntgenstrahlen 10 aufweist, die durch das Austrittsfenster 9 austreten. Der Targetkopf wird durch eine Kühlflüssigkeit gekühlt, die durch die Rohre 17 in einen Kühlraum ein- bzw. austritt. Der Kolben der Röntgenröhre weist einen Vakuumanschluß 18 auf. Die elektrischen Anschlüsse für die Fokussierspule 5 und die Ablenkspulen 6 sind mit 19 bis 22 bezeichnet. Zwischen den beiden Teilen 1 und 2 des Kolbens der Röntgenröhre befindet sich eine Trennwand (Anode) 24, welche mit einer Durchlaßöffnung 25 für den Elektronenstrom 11 versehen ist.The piston of the X-ray tube consists of two parts 1, 2. Part 1 takes the cathode, consisting of the filament 3, which serves as an emitter for the electron current 11, the contacts 12, 13 for the filament 3 and the base 14 and the control electrode 4, which is also carried by the base 14 and which is connected via the connection contact 15 to a voltage source, not shown. The part 2 serving as the anode accommodates in its interior focusing coils 5, deflection coils 6 provided with an air gap 26 and is provided with the target head 7, which receives the target 8 (the anti-cathode) and a shield 16 in its interior, which provides an opening for has the exit of the X-rays 10 generated at the target 8, which exit through the exit window 9. The target head is cooled by a cooling liquid which enters or exits a cooling chamber through the tubes 17. The piston of the x-ray tube has a vacuum connection 18. The electrical connections for the focusing coil 5 and the deflection coils 6 are designated 19 to 22. Between the two parts 1 and 2 of the piston of the X-ray tube there is a partition (anode) 24, which is provided with a passage opening 25 for the electron current 11.

In Fig. 2 ist in vergrößerter Darstellung der Aufbau von Kathode und Steuerelektrode dargestellt. Über die Anschlußkontakte 12, 13, die in Klemmvorrichtungen 27, 28 für den U-förmig gebogenen Heizfaden (Emitter) 3 enden, wird dem Heizfaden 3 Spannung zugeführt, die diesen Heizfaden zum Glühen bringt. Die beiden Klemmvorrichtungen 27, 28 sind dabei in einer Halterung 29 untergebracht, die mittels des Isolierringes 30 auch das Gitter 4 trägt. Diese Steuerelektrode 4 ist als ein starkwandiger Hohlzylinder ausgebildet, der an seiner einen, den Heizfaden 3 umschließenden Stirnseite einen nach innen gerichteten Vorsprung 34 aufweist, der an seiner Außenseite in Form eines Trichters 31 ausgebildet ist, der einen Öffnungswinkel ß von 100° bis 140°, vorzugsweise 120°, aufweist. Dieser Trichter 31 geht auf seiner Innenseite in eine zylindrische Oberfläche 32 über, die abgerundete Kante 33, über. Im Bereich dieser abgerundeten Kante 33 befindet sich die Ebene 35, in welcher sich derjenige Oberflächenteil des Heizdrahtes 3 befindet, der Elektronen emittiert. Durch die besondere geometrische Ausbildung der Steuerelektrode wird einerseits ein elektrisches Feld erzeugt, welches seinen Spitzenwert in der Achse 36 dort hat, wo die Achse 36 die dem Target zugewandte Oberfläche des Heizdrahtes 3 durchbricht. Andererseits ist durch die besondere geometrische Gestaltung der Steuerelektrode 4 erreicht, daß von allen Oberflächenteilen des Heizfadens 3 mehr Strahlung an die Steuerelektrode abgegeben wird als von demjenigen Ort des Heizfadens, an dem die geometrische Achse die dem Target zugewandte Oberfläche des Heizdrahtes 3 durchbricht. Hierdurch wird die Oberfläche des Heizdrahtes überall gekühlt, jedoch ist die Kühlung am geringsten an demjenigen Ort, an dem die geometrische Achse 36 die dem Target 8 zugewandte Oberfläche der Heizdrahtes durchbricht. Als Durchmesser D des Heizdrahtes wird ein solcher von mehr als 0,17 mm gewählt, der Innenradius Ri der Krümmung ist größer als 0,1 D gewählt. Diese Abmessungen sind erheblich größer als die Abmessungen, die bisher für Feinfokus-Röntgenröhren verwendet werden. Der Innenradius Ri und der Außenradius Ra können aber auch noch erheblich größere Werte aufweisen. - In manchen Fällen ist es zweckmäßig, die massiv wie ein Klotz ausgebildete ringförmige Steuerelektrode 4 noch mit einer zusätzlichen Schürze 37 zu versehen, um die nach außen erfolgende Abstrahlung von Wärme zu vergrößern. Diese Schürze 37 wird zweckmäßigerweise einstückig mit der Steuerelektrode 4 hergestellt und stellt im wesentlichen einen massiven Hohlzylinder dar.2 is an enlarged view of the Structure of cathode and control electrode shown. Via the connection contacts 12, 13, which end in clamping devices 27, 28 for the U-shaped filament (emitter) 3, the filament 3 is supplied with voltage, which makes this filament glow. The two clamping devices 27, 28 are accommodated in a holder 29 which also supports the grating 4 by means of the insulating ring 30. This control electrode 4 is designed as a thick-walled hollow cylinder which has on its one end, surrounding the filament 3, an inward projection 34, which is formed on the outside in the form of a funnel 31, which has an opening angle β of 100 ° to 140 ° , preferably 120 °. This funnel 31 merges on its inside into a cylindrical surface 32, the rounded edge 33. In the area of this rounded edge 33 there is the plane 35, in which the surface part of the heating wire 3 is located that emits electrons. Due to the special geometric design of the control electrode, an electric field is generated on the one hand, which has its peak value in the axis 36 where the axis 36 breaks through the surface of the heating wire 3 facing the target. On the other hand, the special geometric design of the control electrode 4 ensures that more radiation is emitted from all surface parts of the filament 3 to the control electrode than from that location of the filament at which the geometric axis breaks through the surface of the heating wire 3 facing the target. As a result, the surface of the heating wire is cooled everywhere, but the cooling is lowest at the location at which the geometric axis 36 breaks through the surface of the heating wire facing the target 8. The diameter D of the heating wire is chosen to be more than 0.17 mm, the inner radius Ri of the curvature is selected to be greater than 0.1 D. These dimensions are significantly larger than the dimensions previously used for fine focus X-ray tubes. The inner radius Ri and the outer radius Ra can also have significantly larger values. In some cases, it is expedient to provide the ring-shaped control electrode 4, which is solid like a block, with an additional apron 37 in order to increase the outward radiation of heat. This apron 37 is expediently produced in one piece with the control electrode 4 and essentially represents a solid hollow cylinder.

Man kann anstelle des Heizdrahtes 3 auch andere Formen für den Emitter verwenden, z. B. Emitter in den Formen, wie sie in Fig. 5 und 6 dargestellt sind. Diese aus massivem Material hergestellten Emitter werden ebenfalls bis zum Glühen durch durchfließenden Strom erhitzt.You can also use other shapes for the emitter instead of the heating wire 3, z. B. Emitter in the forms as shown in Figs. 5 and 6. These emitters made of solid material are also heated until they glow by current flowing through them.

In Fig. 3 ist das Detail 1 aus Fig. 1 dargestellt, nämlich ein Teil des Targetkopfes 7 und das Target 8 im Querschnitt. Das Target 8 ist als ein massiver Klotz ausgeführt, der eine zylindrische oder sphärische Oberfläche auf der dem Elektronenstrom 11 zugekehrten Seite aufweist.FIG. 3 shows the detail 1 from FIG. 1, namely a part of the target head 7 and the target 8 in cross section. The target 8 is designed as a solid block, which has a cylindrical or spherical surface on the side facing the electron stream 11.

Die Innenseite des Targetkopfes 7 ist mit einer Auskleidung 16 aus Blei versehen. Der Targetkopf 7 weist eine seitliche Durchbrechung auf, die durch das Strahlenaustrittsfenster 9 für die austretenden Röntgenstrahlen 10 verschlossen ist. Die am Target 8 eingestellten Werte sind anhand der Fig. 4 näher erläutert : Parallel zur Röhrenachse 36 verläuft die Elektronenstrahlachse E des Elektronenstrahles mit dem Elektronenstrahldurchmesser De. Der Auftreffpunkt der Elektronenstrahlachse E und der Targetkrümmungsradius R wird so gewählt, daß sich ein Targetwinkel a von maximal 10° ergibt. Da mit den erfindungsgemäßen Maßnahmen an der Kathode bereits ein sehr dünn gebündelter Elektronenstrahl auf das Target 8 fällt, ergibt sich eine sehr geringe Breite BFo des optischen Brennflecks. Bei einer Wahl des Targetwinkels von maximal 10° wird eine sehr hohe Intensität der Röntgenstrahlung erreicht, deren Ursache noch nicht wissenschaftlich geklärt werden konnte. Es wird angenommen, daß hier ähnliche Verhältnisse auftreten, wie sie bei der Totalreflexion in der Optik auftreten.The inside of the target head 7 is provided with a lining 16 made of lead. The target head 7 has a lateral opening which is closed by the radiation exit window 9 for the emerging X-rays 10. The values set on the target 8 are explained in more detail with reference to FIG. 4: The electron beam axis E of the electron beam with the electron beam diameter De runs parallel to the tube axis 36. The point of impact of the electron beam axis E and the target radius of curvature R is chosen so that a target angle a of 10 ° results. Since, with the measures according to the invention, a very thinly focused electron beam already hits the target 8, the optical focal spot width BFo is very small. With a choice of the target angle of a maximum of 10 °, a very high intensity of the X-ray radiation is achieved, the cause of which has not yet been scientifically clarified. It is assumed that conditions similar to those that occur with total reflection in the optics occur here.

Die Glühkathode braucht nicht unbedingt aus einem stromdurchflossenen Draht zu bestehen, sie kann auch indirekt beheizt werden, z. B. induktiv beheizt werden. Auch in diesem Falle ist es wichtig, daß die Querschnittsdimensionen der Glühkathode, die durchaus die Form einer Nadel haben kann, groß gegenüber den Dimensionen der Elektronenaustrittsfläche sind und daß man an der Glühkathode einen Punkt mit einer gegenüber den anderen Oberflächenteilen erhöhten Oberflächentemperatur an der Stelle hat, an der das elektrische Feld zwischen Anode und Kathode seinen höchsten Wert erreicht. Es gibt aber auch Möglichkeiten, die Kathode sowohl direkt durch einen hindurchfließenden Strom als auch zusätzlich indirekt zu beheizen.The hot cathode need not necessarily consist of a current-carrying wire, it can also be heated indirectly, e.g. B. are heated inductively. In this case, too, it is important that the cross-sectional dimensions of the hot cathode, which may well have the shape of a needle, are large compared to the dimensions of the electron exit area and that a point with a higher surface temperature than the other surface parts is present on the hot cathode at which the electric field between anode and cathode reaches its highest value. However, there are also ways of heating the cathode both directly through a current flowing through it and additionally indirectly.

Claims (8)

1. A fine-focus X-ray tube, in the evacuated envelope of which is arranged a bright cathode formed by a wire resistance, and partially surrounded by a rotation-symmetrical control electrode, and an anode equipped with target, electromagnetic electron beam focussing and deflecting devices and an inlet diaphragm, characterised in that the cross-sectional dimensions of the wire (3) of the bright cathode are large in comparison to the dimensions of the electron outlet surface ; and that a device is provided which produces an increased surface temperature at the location at which the electric field between the anode and cathode reaches its highest value.
2. A fine-focus X-ray tube as claimed in Claim 1, characterised in that the device which produces an increased temperature is a good absorber of radiant heat and partially surrounds the bright cathode.
3. A fine-focus X-ray tube as claimed in Claim 1, characterised in that the control electrode (4) consists of a thick-walled component which has the shape of a hollow cylinder provided at the end with an inwardly directed projection whose exterior widens in the manner of a funnel, where said funnel forms an angle of 100° to 140°, and that the point of the bright cathode which is furthest removed from the interior of the control electrode is arranged on the axis of the control electrode in a plane which lies in the region of the lower edge of the funnel-shaped part of the end surface.
4. A fine-focus X-ray tube as claimed in Claim 1, characterised in that the wire (3) of the bright cathode is bent in a U or V format.
5. A fine-focus X-ray tube as claimed in Claim 1, characterised in that the target (8) has a spherically-curved surface and the target angle has a value of between 0° and 10°.
6. A method of forming a micro-focus of the electron emission of an X-ray tube bright cathode, characterised in that a wire (3) is used whose cross-sectional dimensions are large in comparison to the dimensions of the electron outlet surface, that on the wire (3) a zone of increased temperature is provided at the location of the electron outlet surface, and that the electric field is contrived .to be such that it reaches its peak value at this increased temperature zone.
7. A method as claimed in Claim 6, characterised in that the increased temperature zone is provided in that a component (4) which absorbs radiant heat absorbs more radiated heat from all the surface of the wire than from the location of the electron outlet surface.
8. A method as claimed in Claim 6, characterised in that the wire (3) is cooled to differing extents such that the highest surface temperature of the wire (3) prevails at the location of the electron outlet surface.
EP83105571A 1982-06-16 1983-06-07 Fine focus x-ray tube and method for the production of a finely focused electron emission from an x-ray filament cathode Expired EP0096824B1 (en)

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AT83105571T ATE29088T1 (en) 1982-06-16 1983-06-07 FINE FOCUS X-RAY TUBE AND METHOD OF FORMING A MICROFOCUS OF THE ELECTRON EMISSION OF AN X-RAY TUBE GLOW CATHOD.

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DE3222511 1982-06-16
DE3222511A DE3222511C2 (en) 1982-06-16 1982-06-16 Fine focus X-ray tube

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EP0096824A1 EP0096824A1 (en) 1983-12-28
EP0096824B1 true EP0096824B1 (en) 1987-08-19

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JPH0618119B2 (en) 1994-03-09
ATE29088T1 (en) 1987-09-15
DE3222511A1 (en) 1983-12-22
EP0096824A1 (en) 1983-12-28
DE3222511C2 (en) 1985-08-29
US4573186A (en) 1986-02-25
JPS598251A (en) 1984-01-17

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